Enhance Propshaft to compress files during precompilation

propshaft.rb

require "rake"

Rake::Task["assets:precompile"].enhance do
  assembly    = Rails.application.assets
  output_path = assembly.config.output_path

  assembly.load_path.assets.each do |asset|
    asset_path      = output_path.join(asset.digested_path)
    compressed_path = output_path.join(asset.digested_path.to_s + ".br")

    unless compressed_path.exist?
      Propshaft.logger.info "Compressing #{asset.digested_path}"
      `brotli #{asset_path} -o #{compressed_path}`
    end
  end;nil
end if Rake::Task.task_defined?("assets:precompile")